Natural modulations of the ocean carbon sink

El Niño-Southern Oscillation (ENSO) is the main source of year-to-year variability in the atmospheric CO2 growth rate and the ocean carbon sink. During El Niño events, the ocean carbon sink increases by up to 1 PgC/y. A tighter constraint on the magnitude and timing of the ocean carbon sink response is however limited by the relatively sparse coverage of carbon observations in the Equatorial Pacific and by uncertainties in the ocean processes underpinning this response. Here, we investigate the physical and biogeochemical processes controlling the carbon sink response to ENSO, using an ocean model coupled to biogeochemistry (GFDL-MOM6-COBALT) combined with ocean and atmospheric observations. In particular, we explore how satellite OCO-2 glint data, which detect temporal and spatial variations in atmospheric CO2 over the tropical oceans, and atmospheric potential oxygen can provide additional constraints on the magnitude and timing of this ocean carbon sink anomaly. We show that differences in precipitation patterns and meridional advection are key drivers of the differences in the carbon sink response, with implications for our understanding of the global carbon cycle, specifically the partition of anthropogenic carbon between the ocean and land sinks.